Attention to the study of the radiation characteristics of streamer discharges in atmospheric air at pressures of a fraction of a Torr unit is primarily associated with obtaining new data on high-altitude discharges, including red sprites. This paper presents the results of studying the characteristics of the radiation of a streamer discharge in low-pressure air upon initiation of ionization waves (streamers) by a repetitively pulsed barrier discharge. It has been established that at air pressures of Delta p=0.08-3 Torr, the lines of the second positive, first negative, and first positive nitrogen systems have the highest intensities in the wavelength range of Deltaλ=280-900 nm, and their contribution to the spectral radiation energy density depends on the discharge region and pressure. The emission bands of the first positive nitrogen system give the red color of the ionization waves, however, the highest intensities under these conditions are recorded on the lines of the second positive and first negative nitrogen systems. It is shown that when the pressure decreases to 0.04 Torr or less, the spectrum and color of the streamer discharge, while maintaining the amplitude of the voltage pulses, changes significantly. New lines and bands appear in it, including intense lines of atomic hydrogen, which is due to an increase in the reduced electric field strength, respectively, in the electron temperature. This leads to the dissociation of molecular gases that are part of the air, as well as those adsorbed by the chamber walls. Keywords: emission spectra, streamer discharge, air, low pressures.

The conditions for obtaining runaway electron (RE) current pulses with a minimum duration at a subnanosecond breakdown of centimeter gaps filled with air at atmospheric pressure were studied. It is shown that the RE current pulse duration depends on many parameters, such as the cathode form, the magnitude of the interelectrode distance, the diameter of the diaphragm, which is part of the anode, as well as on the size of the receiving part of the collector. It has been established that the use of cathodes with an extended edge having a small radius of curvature, RE current pulses consisting of two peaks of picosecond duration can be recorded. Keywords: runaway electrons, beam current, picosecond pulse duration, subnanosecond breakdown.